This invention relates, in general, to semiconductor devices, and more particularly to a method for selectively forming semiconductor regions on semiconductor substrates.
Methods for selectively forming semiconductor regions have been reported in the past. For the selective deposition of silicon, typically a patterned semiconductor wafer having exposed oxide regions and exposed silicon regions is placed in a chemical vapor deposition (CVD) reactor and exposed to elevated temperature and a chlorine containing silicon source-gas (SiCl.sub.x H.sub.y) and hydrogen. Also, under certain conditions, hydrogen chloride (HCl) gas is used with the chlorine containing silicon source-gas and hydrogen.
In general, by controlling the temperature and pressure of the reactor and the concentrations of the chlorine and silicon sources, the process conditions are such that single-crystal silicon regions form in the exposed silicon regions. These conditions also prevent the build up of polysilicon on the exposed oxide region resulting in the selective formation of single-crystal silicon regions.
Another reported method involves using germane (GeH.sub.4) in place of or in addition to HCl. Under appropriate process conditions, single-crystal silicon or single-crystal silicon-germanium regions form on the exposed silicon regions. The presence of germane competes with the silicon source for nucleation sites on the exposed oxide regions preventing silicon or silicon-germanium from forming on the exposed oxide regions.
These selective growth techniques have several problems. For example, both of the above techniques are sensitive to the ratio of exposed silicon to exposed oxide. This is often termed "load dependent" meaning that as the amount of exposed silicon on a semiconductor wafer increases thereby decreasing the amount of exposed oxide, the thickness uniformity of selectively formed silicon regions across the wafer decreases. Also, the above techniques are sensitive to the characteristics of the exposed passivation regions. Different passivation types such as atmospherically grown oxides, deposited oxides and deposited nitrides require the manufacturer to adjust and fine tune the selective epitaxial growth process parameters depending upon the types of passivation films present on the wafer. This significantly impacts manufacturing throughput and cost. In addition, the above techniques are susceptible to faceting defects.
Thus, a need exists for a selective epitaxial growth process that is not load dependent, that does not require a manufacturer to make process adjustments depending upon the type of exposed passivation layer present, and that is less susceptible to faceting defects.